Fiber optic sensors are widely used due to their light weight, miniature dimensions, low power consumption, electromagnetic interference resistance, high sensitivity, wide bandwidths and environmental ruggedness in combination with low cost and well developed fabrication techniques. Among fiber optic sensors, Fabry-Perot based pressure transducers are widely used for localized measurements free of a measurand disturbance. This type of sensor detects changes in optical path length induced by a change in the refractive index or a change in physical length of the Fabry-Perot cavity. The Fabry-Perot sensors are attractive for their miniature size, low cost of the sensing element, and compatibility with low coherence light sources, such as light emitting diodes.
In Fabry-Perot cavity based sensors, pressure is measured by detecting deflection of a membrane to which the pressure is applied. By using the optical measurements, a remote data acquisition may be achieved without loss of signal-to-noise ratio.
Shown in FIG. 1, is a co-axial configuration of fiber pressure sensor which has a Fabry-Perot cavity 10 formed at the end of the optical fiber 12. The cavity 10 is surrounded by a housing 14 and is covered by a diaphragm 16. In this co-axial configuration, the optical characteristics of the light traveling along the fiber optical guide channel 18 are responsive to the pressure field having a direction parallel to the optical axis of the fiber. These co-axially configured fiber sensors are not surface-mountable.
It would be highly desirable to combine the attractive characteristics of the fiber based ultra-miniature pressure sensors with the ability of being surface-mountable to sense and measure pressure fields directed perpendicularly to the surface.